In the related art, to know the growth state of crops, such as rice, wheat, and soybeans, for fertilization control, water volume control, and the like, a light source, such as a laser diode, illuminates the crops with measuring light, and reflected light is calculated and analyzed to measure the nitrogen content in the crops and the like. This measurement is performed by a measurement device mounted in a movable body, such as a tractor and a small Unmanned Aerial Vehicle (UAV), a hand-held measurement device carried by an operative, or the like.
A measurement device in the related art has a narrow measurable range and can perform measurement at a limited distance only, so that a single measurement device cannot perform measurement freely at short to long distances.
Thus, a measurement device having an appropriate measurable range is required depending on the distance (altitude) to crops to be measured. This indicates that multiple measurement devices are required, resulting in an increase in cost and complex work.